Digital receiver coil with built-in received phase noise indicator

ABSTRACT

A system and method synchronizes a digitizer clock of a Magnetic Resonance Imaging (MRI) device with a system clock of an imaging device. In a first method, an original reference signal is split into first and second reference signals in which the second reference signal is phase shifted to generate an orthogonal reference signal. A reliability of image data may be determined based upon a product between the first reference signal and the orthogonal reference signal. In a second method, a reference signal is transmitted from the imaging device to the MRI device and a return signal is received from the MRI device to the imaging device. A discrepancy between the digitizer clock and the system clock may be determined based upon the return signal which includes a variable time delay.

The present application is a divisional of U.S. patent application Ser.No. 15/510,327 filed Mar. 10, 2017 which is the U.S. National Phaseapplication under 35 U.S.C. 371 of International Application No.PCT/IB2015/057122, filed Sep. 16, 2015 which claims the benefit of U.S.Provisional Application Ser. No. 62/055,273 filed Sep. 25, 2014. Theseapplications are hereby incorporated by reference herein.

A magnetic resonance imaging (MRI) device is used to visualize internalstructures of a body. Specifically, MRI makes use of the property ofnuclear magnetic resonance (NMR) to image nuclei of atoms inside thebody. A conventional MRI device includes a retractable patient table inwhich a patient lies. The patient is moved within the MRI device suchthat a large, powerful magnet generates a magnetic field that is used toalign the magnetization of some atomic nuclei in the body, and radiofrequency magnetic fields are applied to systematically alter thealignment of this magnetization. This causes the nuclei to produce arotating magnetic field detectable by the scanner. This information isrecorded to construct an image of the scanned area of the body.

The MRI device has had changes in its operation to improve efficiency inperforming a scan. Specifically, the MRI device may include wirelesscoils that remove the requirement for cable connections. The wirelesscoils enable a significant work flow benefit as the need to connect anddisconnect the cables is eliminated. The use of the wireless coilstypically does not require any reduction in bore size of the MRI devicesuch that an increased coil density may also be realized aboveconventional norms. However, in a substantially similar manner as withany wireless system, signal propagation may undergo various inadvertenteffects such as phase error that may fundamentally change calculationsbeing performed for the scan. In one example, a clock of the MRI devicemay not be properly synchronized with a system clock in which thecalculations are based.

Accordingly, it is desirable to determine and/or synchronize a digitizerclock of the MRI device to more accurately perform the MRI scan. Thus,there is a need for a system that provides an indication or a fixedsignal for the scan to be performed.

FIG. 1 shows a system for a scan room according to the exemplaryembodiments.

FIG. 2 shows an imaging device according to the exemplary embodiments.

FIG. 3 shows a MRI device according to the exemplary embodiments.

FIG. 4 shows an indicator device for generating an indication of adiscrepancy in a digitizer clock of the MRI device according to theexemplary embodiments.

FIG. 5 shows a synchronization flow for adjusting a digitizer clock ofthe MRI device according to the exemplary embodiments.

FIG. 6 shows a method of indicating a discrepancy in a digitizer clockof the MRI device according to the exemplary embodiments.

FIG. 7 shows a method of adjusting a digitizer clock of the MRI deviceaccording to the exemplary embodiments.

FIG. 8 shows a specific synchronization flow for adjusting a digitizerclock of the MRI device according to the exemplary embodiments.

The exemplary embodiments may be further understood with reference tothe following description of the exemplary embodiments and the relatedappended drawings, wherein like elements are provided with the samereference numerals. The exemplary embodiments are related to a systemand method of performing a MRI scan using a MRI device includingwireless coils in which a digitizer clock of the MRI device is firstanalyzed based upon a system clock. Specifically, in a first mechanism,the digitizer clock may be analyzed to provide an indication as to areliability of the MRI scans that would result based upon currentconditions of the digitizer clock. In a second mechanism, the digitizerclock may be analyzed to provide a fixed signal to synchronize thedigitizer clock with the system clock. The MRI procedure, the MRIdevice, the wireless capability, the digitizer and system clocks, theindication, the synchronization, and related methods will be explainedin further detail below.

FIG. 1 shows a system for a scan room 100 according to the exemplaryembodiments. The scan room 100 is used for a patient who requires animaging to be performed. For example, the patient may require a MRI tobe performed on a specific body portion. The scan room 100 includes aMRI device 105 which has a patient table 110, a control panel 115 andMRI components 120 as well as an operator room 125 including an imagingdevice 130.

According to the exemplary embodiments, the MRI device 105 may performthe scan on a patient lying on the patient table 110. Specifically, theMRI device 105 may utilize the MRI components 120 to perform the scan.The patient may be moved within a bore of the MRI device 105 via inputsreceived on the control panel 115. The control panel 115 may allow anoperator to move the patient table 110 for an alignment to be performedwhere the patient table 110 is moved to the isocenter (the point inspace through which the central beam of radiation is to pass).

The MRI components 120 may include a variety of components such as amagnet, gradient coils, radio frequency (RF) coils, and a RF detector.The magnet produces a strong magnetic field around an area to be imagedfor the imaging procedure. This magnetic field allows nuclei (e.g.,hydrogen nuclei of water molecules) to align with a direction thereof.The gradient coils may be disposed within the magnet to produce agradient in the magnetic field in various directions (e.g., X, Y, andZ). The RF coil may be disposed within the gradient coils to produce afurther magnetic field necessary to rotate the spins by various angles(e.g., 90°, 180°, etc.) selected by a pulse sequence. Thus, a radiofrequency signal emitted by excited hydrogen atoms in the body may bedetected using the energy from the oscillating magnetic field applied atthe appropriate resonant frequency. The orientation of the image may becontrolled by varying the magnetic field produced by the magnet usingthe gradient coils and a contrast between tissues is determined by arate at which the excited nuclei return to an equilibrium state.Specifically, the RF detector may receive these energy measurements andprovide the data to the imaging device 130 for processing to ultimatelygenerate the images of the scan.

A conventional MRI device utilizes cable connections for the gradientand RF coils that are connected and reconnected when used. In contrast,the exemplary embodiments relate to utilizing the MRI device 105 inwhich wireless coils are used. Specifically, the cabling to the gradientand RF coils may be replaced with a wireless link. An example of such awireless link may be a single frequency Multiple Input Multiple Output(MIMO) microwave link. The MRI components 120 of the MRI device 105 mayinclude a frequency up-converter for each coil and an array oftransceivers in the bore of the MRI device 105. Specifically, the MRIcomponents 120 may be configured such that the transceivers areconnected to an array of antennas that are integrated into the bore. TheMRI components 120 may include a local oscillator that generates asignal in the transceivers that may feed the antenna array to illuminatethe coil electronics. The signal from the local oscillator may alsoconvert the microwave signals received from the coils back to theoriginal selected magnetic resonance frequency. This may be packaged asthe data to be received by the imaging device 130 for processing togenerate the image from the scan.

In view of this wireless mechanism used by the MRI device 105, thesignals transmitted to generate the data that the imaging device 130bases the processing for image generation is subject to variousinterference and other effects that alter the reliability of the data.For example, as in any digital receiver systems, phase noise on thedigitizer clock of the MRI device 105 may translate into reduced qualityand/or reduced reliability of the reconstructed image. With particularregard to wireless coils in the MRI device 105, the digitizer clock issynchronized over a wireless channel with the risk of adding impairmentsto the clock signal. Those skilled in the art will understand that thedigitizer clock provides a baseline in which the signals are propagatedsuch that when the digitizer clock is out-of-sync with a system clock,the resulting data may become more unreliable as a higher discrepancyexists between the digitizer and system clocks. Therefore, the exemplaryembodiments provide a mechanism to insure a quality of service byincluding hardware and/or software components to a digital receiver coilthat enables measurement of a reference signal or a Received Phase NoiseIndicator (RPNI) which is discussed in further detail below. As willbecome more evident below, the reference signal and the RPNI may besimilar to a Received Signal Strength Indicator in wireless systems infunctionality although more defined and specific to the wireless MRIdevice 105.

As those skilled in the art will recognize, MRI is an imaging methodthat uses frequency and phase encoding of protons (e.g., hydrogen nucleiin water molecules) for image reconstruction. In a particular examplewhere synchronization of the digitizer clock may be highly relevant,phase noise on the digitizer clock may cause image artifacts due to thenature of the encoding method, particularly during longacquisitions/scans. Accordingly, it may be of importance to have thedigitizer clock that minimizes a Root Mean Square (RMS) phase error onthe digitized signal. For example, if the digitizer clock induced RMSphase error in the image raw data is to be set to below 1 degree, theRMS time jitter should preferably stay below 44 picoseconds (ps) at 64MHz and below 22 ps at 128 MHz. As discussed above, the conventional MRIdevice may use a digitizer clock that is synchronized using wire oroptical fiber to a highly stable system clock. However, with thewireless MRI device 105, the digitizer clock synchronization isperformed wirelessly which poses the above issues, particularly withsignal purity and subsequent reliability.

More specifically, the digitizer clock may be synchronized bytransmitting a carrier signal as a pilot tone from the imaging device130 to the MRI device 105. For example, the pilot tone may be thereference signal or the RPNI. The MRI device 105 may include circuitrywithin the MRI components 120 that amplifies the pilot tone which isthen filtered and used to synchronize a Phase-Locked-Loop (PLL) circuit.The phase noise Φr(t) of the recovered clock signal can be a combinationof the phase noise Φp(t) of the received pilot signal and the phasenoise generated by the PLL. Any impairments in the channel or in theclock recovery circuit (e.g., PLL) may add phase noise to the recoveredclock. Some of these impairments may be caused by patient motion (e.g.,interference) or distortion of the wireless pilot tone channel. Otherimpairments may be due to hardware malfunction in the clock recoveryunit. Any of these issues with digitizer clock synchronization may leadto poor and unreliable image quality and potential service calls/scannerdown time. Early detection of poor phase noise performance may lead toearly preventive and corrective actions to improve customer satisfactionof the MRI device 105. For example, the scanner personal/operator may beadvised to monitor patient motion or field service may be informedregarding a deteriorating RPNI prior to image degradation.

According to the exemplary embodiments, the imaging device 130 maygenerate the RPNI and transmit it to the MRI device 105 to synchronizethe digitizer clock. In a first manner, the MRI device 105 may include amechanism that utilizes the reference signal to determine an accuracy ofthe digitizer clock by performing a calculation. The reference signalmay be a signal based upon a system clock that forms a basis forsynchronization. A result of this calculation may be a discrepancy thatindicates whether the data provided by the MRI device 105 to the imagingdevice 130 is reliable for image generation. There may be predeterminedthresholds for the discrepancy such that when beyond one of thesethresholds, the MRI device 105 may be prevented from performing a scanwhen the image degradation would be too high and unacceptable.Accordingly, this first manner may relate to a relatively short-termmechanism. In a second manner, the MRI device 105 may include amechanism that utilizes the RPNI by calculating a phase offset for theclock signal that will compensate the phase error due to, for example,variable time delays in the wireless channel. The reference signal mayfirst be converted, transmitted, and returned as a return signalundergoing variable time delays which is processed to generate the RPNI.The imaging device 130 may subsequently calculate a clock phase offsetthat would synchronize the digitizer clock properly. Accordingly, thissecond manner may relate to long term phase stability between a systemclock and a receiver clock.

FIG. 2 shows the imaging device 130 of FIG. 1 according to an exemplaryembodiment. As discussed above, the imaging device 130 may be configuredto communicate wirelessly with the MRI device 105. Accordingly, theimaging device 130 may include a receiver 225 and a transmitter 230.However, it should be noted that the imaging device 130 may include acombined transceiver to provide the functionalities of the receiver 225and the transmitter 230. The receiver 225 and the transmitter 230 may befor a short range wireless communication since the imaging device 130 isoften in close proximity to the MRI device 105 (e.g., both within thescan room 100). However, as will be described in an example below, thereceiver 225 and the transmitter 230 may also be configured for longrange wireless communications such as with a network.

Also as discussed above, the imaging device 130 may be configured toprovide the RPNI that is used by the MRI device 105 to synchronize thedigitizer clock. The imaging device 130 includes a processor 205 and amemory arrangement 210. The processor 205 may execute a system clockapplication 235 that maintains the system clock forming the basis onwhich the digitizer clock is synchronized. In a first manner, the systemclock application 235 may be configured to solely maintain the systemclock in a stable manner. In a second manner, the system clockapplication 235 may be configured to utilize the receiver 225 and thetransmitter 230 that are capable of wireless communications to request asynchronization of the system clock. In either manner, the system clockmay be maintained and used for synchronization functionalities.

The processor 205 may also execute a synchronization application 240.The synchronization application 240 may include a functionality togenerate the RPNI based upon the system clock application 235. The RPNImay be generated by the synchronization application 240 and transmittedto the MRI device 105 via the transmitter 230. As will be described infurther detail below, the synchronization application 240 may furthergenerate a fixed RPNI that represents the long term phase drift betweensystem clock and receiver clock. The fixed RPNI may be based upon thereference signal and information determined from a return signalprovided by the MRI device 105 upon processing of the reference signal.The memory arrangement 210 may include a synchronization parameterlibrary 245. The synchronization parameter library 245 may includepre-calculated parameters on which the reference signal is to be fixedto generate the RPNI. For example, the synchronization parameter library245 may be a table of data from which the determined informationprovides the necessary operations to generate the RPNI. Thesynchronization parameter library 245 may be pre-programmed into theimaging device 130.

The imaging device 130 may also include a display device 215 and aninput device 220. For example, the processor 205 may also execute animage generation application that utilizes the data received from theMRI device 105 (via the receiver 225) to generate the images of thescan. These images may be shown on the display device 215. The inputdevice 220 may receive inputs from the operator to control operation ofthe MRI components 120 to select a slice to be scanned for the image tobe generated.

FIG. 3 shows the MRI device 105 of FIG. 1 according to the exemplaryembodiments. As discussed above, the MRI device 105 may be configured tocommunicate wirelessly with the imaging device 130. Accordingly, the MRIdevice 105 may include a receiver 325 and a transmitter 330. It shouldagain be noted that the MRI device 105 may also include a combinedtransceiver to provide the functionalities of the receiver 325 and thetransmitter 330. The receiver 325 and the transmitter 330 may be for ashort range wireless communication with the imaging device 130. Althoughunlikely to require long range communication, the receiver 325 and thetransmitter 330 may also be configured for this purpose.

Also as discussed above, the MRI device 105 may be configured to receivethe RPNI from the imaging device 130 to compensate the phase offsetbetween the digitizer clock and the system clock. The MRI device 105includes a processor 305 and a memory arrangement 310. The processor 305may execute a digitizer clock application 335 that maintains thedigitizer clock and thus forming the basis on which signals andoscillations are controlled in the wireless gradient and RF coils. Thus,when the MRI device 105 receives the RPNI, the digitizer clockapplication 335 may apply the information thereof to correct the phaseerror between the digitizer clock and the system clock. The digitizerclock application 335 may further provide the return signal fromprocessing the reference signal such that the RPNI may be received.

The processor 305 may also execute an indicator application 345. Theindicator application 345 may operate in conjunction with the indicatordevice 340. As will be described in further detail below, the indicatordevice 340 may receive the reference signal to determine a discrepancybetween the digitizer clock and the system clock. Depending on a resultfrom the indicator device 340, the indicator application 345 may providea corresponding indication as to a reliability of the data fromperforming a scan to generate the images on the imaging device 130.

The MRI device 105 may also include the MRI components 120, a displaydevice 315, and an input device 320. For example, when moving thepatient on the patient table 110 into the bore of the MRI device 105,the control panel 115 may include the display device 315 and the inputdevice 320 for proper alignment with the isocenter.

As discussed above, a first manner of utilizing the reference signal isfor a relatively short-term mechanism. Specifically, the indicatordevice 340 may receive the reference signal to provide discrepancyinformation to the indicator application 345. It should be noted thatthe indicator device 340 is only exemplary and the MRI device 105 mayinclude any combination of software and hardware to provide theindications described below. FIG. 4 shows the indicator device 340 ofthe MRI device 105 for generating an indication of a discrepancy in adigitizer clock of the MRI device according to the exemplaryembodiments.

Those skilled in the art will understand that there are many ways todetect phase noise. A highly sensitive and accurate method may beimplemented in phase noise test equipment when measuring phase noise inwireless systems that are designed for a highest phase noise sensitivityover a very large frequency range. As discussed above, when related towireless coils in the MRI device 105, there are several differencesbetween signals of wireless systems and wireless MRI devices such as theMRI device 105. For example, with wireless coils in the MRI device 105,the phase noise of a single sinusoidal signal is of interest. Thissignal is not even required to be the actual analog digital converter(ADC) clock signal itself but may also be a multiple in frequency. Thatis, when multiplying a frequency, the phase noise increases linearlywith the product. For example, if a 50 MHz signal with a 1 degree jitteris multiplied by a factor of 10, a 500 MHz signal with a 10 degreejitter results. Thus, those skilled in the art will recognize that it isadvantageous to measure the phase noise at a multiple of the clockfrequency due to increased sensitivity.

The indicator device 340 may include components configured for thispurpose. Specifically, the indicator device 340 may detect a discrepancyor a phase by multiplying a signal with an orthogonal signal of itself.Although the digitizer clock may be designed to identically follow thesystem clock, there is some discrepancy that results, particularly overa large period of time and/or with interference (e.g., a patientmoving). When the digitizer clock is completely synchronized with thesystem clock where there is no jitter, a product of an orthogonal signalto an original signal results as zero indicating no discrepancy. Forexample, with oscillations, a pure sine wave is exhibited such that anorthogonal signal is a pure cosine wave where the two waves negate eachother. However, when a discrepancy exists, the sine wave is altered sothat the orthogonal signal results in some non-zero value.

To accomplish this, the indicator device 340 includes a frequencymultiplier 405 that receives the reference signal. It should be notedthat the frequency multiplier 405 is only exemplary and is not required.The reasons for including a frequency multiplier were discussed above.Subsequently, the signal is sent to a splitter 410 that generates afirst signal that is sent to a multiplier 420 and a second identicalsignal that is sent to a phase shifter 415. To reach the orthogonalsignal, the phase shifter 415 may shift the phase by 90 degrees. Thephase shifter 415 sends the orthogonal signal to the multiplier 420.After multiplying, the result is sent to a low pass (LP) filter 425 suchthat the multiplied frequency signal is attenuated for the detector 430to output the discrepancy value. Again, if the signal and the orthogonalsignal are truly orthogonal (i.e., no jitter), then the product is zero.However, if there is any jitter on the reference signal, then it causesa residual signal that is indicative of the received phase noise.

The indicator application 345 of the MRI device 105 may receive theresidual signal from the indicator device 340. Referring to theindicator parameter library, the indicator application 345 may determinea reliability of the data obtained from performing a scan. The indicatorparameter library may define a plurality of ranges in which thediscrepancy corresponds from the residual signal. In a first range fromzero to a first value, the residual signal may be sufficiently negligentthat the reliability of the data is satisfactory for image generation.In a second range from the first value to a second value, the residualsignal may be sufficiently large to affect the image generation. In sucha scenario, the indicator application 345 may provide an indication onthe display device 215 and/or 315 that the data may be not as reliablecompared to when the residual signal is within the first range. In athird range from the second value to a maximum value, the residualsignal may be sufficiently adverse that the image generation isunreliable. In such a scenario, the indicator application 345 mayprovide an indication on the display device 215 and/or 315 that the datamay be unreliable. The indicator application 345 may also perform otherfunctionalities. For example, the indicator application 345 may transmita signal that deactivates the MRI device 105. In another example, theindicator application 345 may transmit a notification to a technician toaddress the discrepancy.

It should be noted that the relatively short-term mechanism of the firstmanner may be utilized in a variety of ways. For example, this mannerprovides a cost efficient way of determining phase noise. The indicatordevice 340 and/or the indicator application 345 may be incorporatedwithin the MRI device 105 or may be modular and separately connected tothe MRI device 105. Accordingly, the first manner may be easilyincorporated into a MRI device using wireless coils that does notalready have a wireless synchronization functionality. Through the firstmanner, a wired connection may subsequently be utilized when theresidual signal indicates a need for synchronization of the digitizerclock. In another example, this may be used in conjunction with thesecond manner which is described below.

As discussed above, a second manner of utilizing the RPNI is for arelatively long-term mechanism. Specifically, the synchronizationapplication 240 may transmit the reference signal to receive a returnsignal from the MRI device 105 to determine the RPNI that synchronizesthe digitizer clock of the MRI device 105 to the system clock of theimaging device 130. It should be noted that the imaging device 130 isonly exemplary and this component or any other component may be used toprovide the functionalities described below. FIG. 5 shows asynchronization flow 500 for adjusting a digitizer clock of the MRIdevice 105 according to the exemplary embodiments. It should also benoted that the synchronization flow 500 is also only exemplary and anyoperation to determine a fix for the reference signal to generate theRPNI may be used. For example, a more specified embodiment for thesynchronization flow will be described below with regard to FIG. 8.

The synchronization flow 500 utilizes a round trip phase errorcorrection. Being a round trip, any variable phase error across achannel 505 between the imaging device 130 and the MRI device 105appears twice during a round trip of the reference signal. Thus, ameasurement of the phase drift of the round trip signal at the imagingdevice 130 and halving it provides information about the phase drift atthe MRI device 105. This information may subsequently be used ingenerating the RPNI to correct any phase error due to the digitizerclock of the MRI device 105 not being synchronized with the systemclock.

The system clock application 235 of the imaging device 130 may include afrequency conversion functionality whereas the digitizer clockapplication 335 of the MRI device 105 may include an opposing frequencyconversion functionality. As discussed above, the MRI device 105 mayinclude a PLL that utilizes a reference signal to generate a multiple ofthat frequency that may also be divided down. Accordingly, the frequencyconversion functionality may include first multiplying the referencesignal with a first value to obtain a first result signal and seconddividing the first result with a second value to obtain a second resultsignal. This second result signal may be output and transmitted via thetransmitter 230 of the imaging device 130. The second result signal maytravel through the channel 505 in which a variable time delay becomesincorporated into the output to obtain an altered second result signal.The variable time delay may include a variety of components. Forexample, the variable time delay may include a delay added by thechannel 505, a drift error added to the signal, a combination thereof,etc.

When attempting to synchronize the digitizer clock, the MRI device 105may perform the opposing frequency conversion functionality on thereceived altered second result signal. Thus, the opposing frequencyconversion functionality may include first multiplying the alteredsecond result signal by the second value to obtain a third result signaland dividing the third result signal by the first value to obtain afourth result signal. The fourth result signal may be used by thedigitizer clock application to synchronize the digitizer clock.

However, the exemplary embodiments may provide for the altered secondresult signal to have a further frequency conversion operation performedthereon. Specifically, the altered second result signal is multiplied bya third value to obtain a fifth result signal and divided by a fourthvalue to obtain a sixth result signal. The sixth result signal maytravel through the channel 505 in which the variable time delay againbecomes incorporated into the output to obtain an altered sixth resultsignal. In this manner, the variable time delay has been added twice inthe round trip.

The imaging device 130 may process the altered sixth result signal todetermine a fix to be applied to the RPNI for the digitizer clock to besynchronized with the system clock. That is, the fix may eliminate anyjitter, phase error, etc. Specifically, halving the resulting variabletime delay provides the necessary information to the synchronizationapplication 240 to determine the fix. The RPNI that was originallytransmitted may be sufficient when a wired connection is available.However, with the introduction of the variable time delay, thesynchronization application 240 may generate the RPNI that considers thevariable time delay such that even after the variable time delay isexperienced in the channel 505, the digitizer clock application 335 mayutilize the RPNI to synchronize the digitizer clock with the systemclock.

In a specific embodiment, a reference signal sin(ω₀·t) may undergo thefrequency conversion to result in an output signal

$\sin \left( {{\frac{A}{B}{\omega_{0} \cdot t}} + \phi_{1}} \right)$

by the imaging device 130. After traveling through the channel 505, theMRI device 105 may be provided a received signal

$\sin \left( {{\frac{A}{B}{\omega_{0} \cdot \left( {t - t_{c} - {\Delta \; t}} \right)}} + \phi_{1}} \right)$

where the variable time delay includes a channel delay t_(c) and a drifterror Δt. The MRI device 105 may perform the further frequencyconversion operation on the received signal to generate a further outputsignal

$\sin \left( {{\frac{A}{B}\frac{C}{D}{\omega_{0} \cdot \left( {t - t_{c} - {\Delta \; t}} \right)}} + {\frac{C}{D}\phi_{1}} + \phi_{2}} \right)$

by the MRI device 105. After traveling through the channel 505, theimaging device 130 may be provided a further received signal

$\sin \left( {{\frac{A}{B}\frac{C}{D}{\omega_{0} \cdot \left( {t - {2t_{c}} - {2\; \Delta \; t}} \right)}} + {\frac{C}{D}\phi_{1}} + \phi_{2}} \right)$

with the same variable time delay. After performing an oppositefrequency conversion on the further frequency conversion operationperformed by the MRI device 105, an output signal

$\sin \left( {{\omega_{0} \cdot \left( {t - {2t_{c}} - {2\Delta \; t}} \right)} + {\frac{B}{A}\phi_{1}} + {\frac{B}{A}\frac{D}{C}\phi_{2}}} \right)$

may be obtained. This output signal may provide the basis fordetermining the fix to be applied to the RPNI signal to generate theRPNI signal transmitted to the MRI device 105. As described above, theRPNI signal may have an opposing frequency conversion operationperformed thereon to determine the manner in which to synchronize thedigitizer clock with the system clock.

As discussed above, FIG. 8 is a particular embodiment for thesynchronization filter and accompanying components. Specifically, FIG. 8shows a specific synchronization flow 800 for adjusting a digitizerclock of the MRI device 105 according to the exemplary embodiments. In asubstantially similar manner as the synchronization flow 500 of FIG. 5,the synchronization flow 800 relates to a round trip phase errorcorrection. That is, a signal may be generated from an imaging device130 that is received by the MRI device 105 in which the MRI device 105“processes” the signal to generate a return signal. The return signalmay be used by the imaging device 130 to determine a phase correction tobe applied for any signals transmitted from the imaging device 130 tothe MRI device 105. Specifically, the above mechanism described withregard to the synchronization flow 500 may again be utilized withrespect to the synchronization flow 800.

As illustrated, the synchronization flow 800 may again include theimaging device 130 and the MRI device 105. Although the imaging device130 and the MRI device 105 and corresponding components were describedabove, the synchronization flow 800 again describes these components butwith regard to the particular embodiment herein. Thus, the imagingdevice 130 may include an oscillator (OSC) 805, a bandpass filter 810, atransceiver 815, a bandstop filter 820, a Costas loop 825, a phasecomparator 830, and a resulting phase correction value 835. The MRIdevice 105 may include a transceiver 840, a bandpass filter 845, aCostas loop 850, a numerically controlled oscillator (NCO) 855, adigital to analog converter (DAC) 860, and a bandstop filter 865.

Those skilled in the art will understand the functionalities associatedwith the components of the imaging device 130 and the MRI device 105.For example, the bandpass filter may be a device that passes frequencieswithin a predetermined range and rejects other frequencies whereas thebandstop filter provides a substantially opposite functionality. Inanother example, the Costas loop may be a particular PLL based circuitused for carrier phase recovery from suppressed-carrier modulationsignals. In a further example, the NCO may be a digital signal generatorcreating a synchronous, discrete-time, discrete-valued representation ofa waveform (e.g., sinusoidal).

As illustrated, the OSC 805 may be predefined to generate signals at aspecified frequency such as 10 MHz. Initially, this 10 MHz signal may befed to the bandpass filter 810 prior to transmission by the transceiver815 to the imaging device 105. Thus, the transceiver 840 of the MRIdevice 105 may receive a signal from the imaging device 130 at 10 MHz.The received 10 MHz signal may pass through the bandpass filter 845prior to processing at the Costas loop 850. Once processed, the signalmay be fed to the NCO 855. The NCO 855 may output an effected signalsuch as one that may be ±1 MHz above and below the incoming 10 MHzsignal. That is, the DAC 860 may receive a 9 MHz and a 11 MHz signal.These signals may be provided to the bandstop filter 865 prior totransmission by the transceiver 840 back to the imaging device 130. Thisway, both signals propagating through the channel, from transceiver 815to transceiver 840, and vice versa from transceiver 840 to transceiver815, are centered on 10 MHz, and therefore both signals will experiencethe same channel delay that corresponds to the variable channel propertyfor that frequency.

When the imaging device 130 receives the return signals at 9 MHz and 11MHz from the MRI device 105 via the transceiver 815, these signals mayinitially go through the bandstop filter 820 prior to processing at theCostas loop 825. The phase comparator 830 may receive the output fromthe Costas loop 825 as well as receive the original signal from theoscillator 805 which may serve as a reference to determine the phasecorrection value 835. In this manner, the phase correction value 835 maybe determined which may be used to synchronize the digitizer clock withthe system clock.

FIG. 6 shows a method 600 of indicating a discrepancy in a digitizerclock of the MRI device 105 according to the exemplary embodiments. Themethod 600 relates to the first manner in which a relatively short-termmechanism is provided to generate an indication of a reliability of thedata obtained from performing a scan based upon current conditionsexisting on the digitizer clock. The method 600 will be described withregard to the MRI device 105, the indicator device 340, and theindicator application 345.

In step 605, the MRI device 105 receives a reference signal.Specifically, via the receiver 325, the frequency multiplier 405 of theindicator device 340 receives the reference signal. In step 610, thefrequency multiplied reference signal is split into two identicalsignals, a first one being sent to the multiplier 420. In step 615, thesecond split signal is sent to the phase shifter 415 such that the phaseis shifted orthogonal to the original signal. As discussed above, thephase shifter 415 may have various values such as Π/2+N*Π, where N is apositive integer in which a larger the value N results in a longer timedelay between the two signals. In this manner, different parts of thephase noise spectrum may be tested. However, it should be noted that itmay be difficult to generate significantly long phase delays between thetwo split signals, in particular, phase drift that happens over longperiods of time (e.g., seconds to minutes) may require a differentmechanism. Such a different mechanism may be the probing the long termphase drift, a method for which is discussed in further detail below asa roundtrip phase error compensation. In step 620, the orthogonal signalis also sent to the multiplier such that the original signal and theorthogonal signal are multiplied. Subsequently, the output may be sentto the LP filter 425 and the detector 430.

In step 625, the indicator application 345 receives the product anddetermines if there is a residual signal. As discussed above, if thedigitizer clock is properly synchronized with the system clock wherethere is no jitter, the product results as zero. Thus, when there is noresidual signal, the indicator application 345 continues the method 600to step 630 where an indication of no phase noise is provided, forexample, on the display device 215 and/or 315. Such an indication mayindicate that the data used to generate the images is very reliable.

Returning to step 625, if the indicator application 345 determines thatthere is a residual signal, it continues the method 600 to step 635. Instep 635, the indicator application 345 determines whether the residualsignal is above a predetermined threshold that may be stored in theindicator parameter library 350. If the residual signal exists but isbelow the predetermined threshold, the indicator application 345continues the method 600 to step 640. In step 640, the indicatorapplication 345 provides an indication that there is a phase noise butis within acceptable limits where the data used to generate the image isstill reliable. However, if the residual signal exists and is above thepredetermined threshold, the indicator application 345 continues themethod 600 to step 645. In step 645, the indicator application 345provides an indication that there is sufficient phase noise that thedata used to generate the image is unreliable.

It should be noted that the method 600 may include further steps. Forexample, as discussed above, when the indication of phase noise in theresidual signal is above the predetermined threshold, the indicatorapplication 345 may perform a variety of subsequent actions such asdeactivating the MRI device 105, contacting a technician, etc. Inanother example discussed above, there may be multiple thresholds forthe residual signal.

FIG. 7 shows a method 700 of adjusting a digitizer clock of the MRIdevice 105 according to the exemplary embodiments. The method 700relates to the second manner in which a relatively long-term mechanismis provided to generate a fixed RPNI signal that synchronizes thedigitizer clock with the system clock such that data obtained fromperforming a scan is reliable in generating images. The method 700 willbe described with regard to the MRI device 105 and the imaging device130.

In step 705, the imaging device 130 generates a reference signal basedupon the system clock maintained by the system clock application 235.Specifically, the synchronization application 240 may generate thereference signal. In step 710, the synchronization application 240converts the frequency of the reference signal. As discussed above, thefrequency conversion operation may entail first multiplying by a firstfactor and then dividing by a second factor as done with a PLL.

In step 715, the imaging device 130 transmits the converted referencesignal via the transmitter 230 to the MRI device 105.

During transmission, the converted reference signal may undergo avariable time delay in the channel 505. As discussed above, such avariable time delay may include a channel delay, a drift error, etc.Thus, the converted reference signal may have been transmitted in afirst way but is received in a second way. Thus, in step 720, the MRIdevice 105 receives the converted reference signal that underwent thevariable time delay via the receiver 325. In step 725, the digitizerclock application 335 of the MRI device 105 converts the delayedconverted reference signal. As discussed above, the further frequencyconversion operation may entail first multiplying by a third factor andthen dividing by a fourth factor. In step 730, the MRI device 105transmits the re-converted reference signal via the transmitter 330 tothe imaging device 130.

During transmission, the re-converted reference signal may again undergothe variable time delay in the channel 505. Thus, the re-convertedreference signal may have been transmitted in a first way but isreceived in a second way. Thus, in step 735, the imaging device 130receives the re-converted reference signal that underwent the variabletime delay via the receiver 225. Specifically, the variable time delayhas been applied twice. In step 740, the imaging device 130 performs anopposing frequency conversion for all the conversions.

In step 745, the imaging device 130 determines a discrepancy from thereference signal being transmitted over the loop. Specifically, thediscrepancy may be based upon half of a total variable time delayapplied in the received return signal. In step 750, the imaging device130 determines a fix to be applied on the reference signal such that thevariable time delay is negated when transmitted to the MRI device 105.That is, the synchronization application 240 generates the RPNI. In step755, the imaging device 130 transmits the RPNI to the MRI device 105. Instep 760, the MRI device 105 receives the RPNI that underwent thevariable time delay in the channel 505. It should be noted that theimaging device may alternatively use the RPNI and correct the phaseoffset of the actual MRI data when the MRI data is transmitted from theMRI device 105 to the imaging device 130. Nevertheless, the RPNI isconfigured for this variable time delay. Thus, in step 765, thedigitizer clock application 335 of the MRI device 105 synchronizes thedigitizer clock with the system clock.

According to the exemplary embodiments, the system and method of theexemplary embodiments provide a mechanism in a MRI device utilizingwireless coils to process a reference signal from an imaging device. TheMRI device may process the reference signal to determine a discrepancybetween a system clock and a digitizer clock such as inclusion ofjitter. The discrepancy may be used as a basis to generate an indicationof reliability of data obtained from performing a scan to generateimages. The MRI device may also process the reference signal throughfrequency conversions and provide a return signal to the imaging device.Using a round trip loop and experiencing a variable time delay twicefrom first traveling through a channel from the imaging device to theMRI device and then traveling again through the channel from MRI deviceto the imaging device, the imaging device may generate a received phasenoise indicator signal based upon the determined delay such that thedigitizer clock may be properly synchronized and phase aligned with thesystem clock. In this manner, the data obtained from performing the scanmay be more reliable in generating images.

Those skilled in the art will understand that the above describedexemplary embodiments may be implemented in any number of manners,including, as a separate software module, as a combination of hardwareand software, etc. For example, the generation of the model of thepatient may be a program containing lines of code that, when compiled,may be executed on a processor.

It will be apparent to those skilled in the art that variousmodifications may be made in the present invention, without departingfrom the spirit or the scope of the invention. Thus, it is intended thatthe present invention cover modifications and variations of thisinvention provided they come within the scope of the appended claims andtheir equivalent.

What is claimed is:
 1. A method, comprising: generating, by an imagingdevice, a reference signal for a Magnetic Resonance Imaging (MRI)device, the MRI device utilizing wireless coils propagating imagesignals based upon a digitizer clock to obtain image data used by theimaging device to generate a MRI image, the reference signal beinggenerated based upon a system clock by which the image signals aredesired to be propagated; transmitting, by the imaging device, thereference signal to the MRI device via a channel, the channel includinga variable time delay; receiving, by the imaging device, a return signalfrom the MRI device via the channel, the return signal including twicethe variable time delay; determining, by the imaging device, adiscrepancy between the digitizer clock and the system clock based uponthe return signal.
 2. The method of claim 1, further comprising:determining, by the imaging device, a fix to be applied on the referencesignal, the fix incorporating the variable time delay of the channel;and generating, by the imaging device, a received phase noise indicator(RPNI) signal that includes the fix, the RPNI signal used by the MRIdevice to synchronize the digitizer clock with the system clock.
 3. Themethod of claim 1, further comprising: performing, by the imagingdevice, a frequency conversion operation on the reference signal priorto the transmitting.
 4. The method of claim 3, wherein the frequencyconversion operation includes a multiplication by a first factor and adivision by a second factor, the first and second factors based upon thesystem clock.
 5. The method of claim 4, wherein the return signal had afurther frequency conversion operation performed thereon prior to thereceiving.
 6. The method of claim 5, wherein the further frequencyconversion includes a multiplication by a third factor and a division bya fourth factor, the third and fourth factors based upon the digitizerclock.
 7. The method of claim 6, further comprising: performing, by theimaging device, an opposite frequency conversion operation and a furtheropposite frequency conversion operation on the return signal, theopposite frequency conversion operation being a division by the firstfactor and a multiplication by the second factor, the further oppositefrequency conversion being a division by the third factor and amultiplication by the fourth factor.
 8. The method of claim 1, whereinthe variable time delay includes one of a channel delay, a drift error,and a combination thereof.
 9. The method of claim 2, wherein thewireless coils include wireless gradient coils and wireless radiofrequency (RF) coils.
 10. An imaging device, comprising: a system clock;a processor configured to generate a reference signal for a MagneticResonance Imaging (MRI) device, the MRI device utilizing wireless coilspropagating image signals based upon a digitizer clock to obtain imagedata used by the imaging device to generate a MRI image, the referencesignal being generated based upon the system clock by which the imagesignals are desired to be propagated; a transmitter configured totransmit the reference signal to the MRI device via a channel, thechannel including a variable time delay; and a receiver configured toreceive a return signal from the MRI device via the channel, the returnsignal including twice the variable time delay, wherein the processor isfurther configured to: determine a discrepancy between the digitizerclock and the system clock based upon the return signal; determine a fixto be applied on the reference signal, the fix incorporating thevariable time delay of the channel; and generate a received phase noiseindicator (RPNI) signal that includes the fix, wherein the transmitteris further configured to transmit the RPNI signal to the MRI device tosynchronize the digitizer clock with the system clock.